Pulse repeating system



Jap. 9, 1945. R. B. SHANCK 2,366,837

PULSE REPEATING SYSTEM Filed July vl0, .1943 3 Sheets-Sheet l E/G. I

EkoM CALL/NG END l FROM CALLED END` FROM CALLED E/vo /N VEN TOR A. B..SHANCK Jan.9,1945. R, B SHANCK 2,366,837

PULSE REPEATING SYSTEM Filed July l0, 1943 5 Sheets-Sheet 2 yI'N VE NTOR R. a. SHA/vak ATTORNEY o `lvatented Jan. 9, 1945 l UNITED STAT ESPATENT OFFICE o PULsEJRfErEAfrING SYSTEM r r Roy B. Shanclr,` Douglas`Manor, NQY., assignor i I to Bell Telephone Laboratories, IncorporatedNew York N. Y., a corporation olf` New York Application July 1ro, 1943,sentano. 494,209V :1u claims. l (Crue-84)" r The invention relates `topulse repeating systems and more particularly to systems 'ot this typeoperating on a duplex basis.

It is an object of the invention to provide a pulse repeating systemwith, a simplied duplex` balanceand capable of eicientoperation under`conditions oi` line` variations and interference Itis a more specificobject of the invention to l provide a system of this type which withstandardizedequipment is adapted for repeating ser lecting andsupervising pulses for telephone switching systems over lines oi greatlydiffering found in the fact that the trafc requirements in-` clude thetransmission 1in both directions over` the line circuit of supervisorysignals or pulses` The operations are complicated by the requirementthatgin the series of operations involved in the setting up ofacconnection, the line circuit is placed under two different conditions,whichmay be termed theidle andthe busy conditions.

The pulse repeating system is adapted to receive dialing pulses from avcalling station, `which `over the line circuit, this relay beingunaected `by outgoing `signals when the impedance bali ance is perfect.For this purpose the polar relay may be connected in anywell-knownmanner as byhaving its windings. directly included .in the twobalancing branches or connected in a bridge between the balancedcircuitsin accordance with r T well-known practice in telegraphrepeatingsystems. .The system is also equippedfor the transmission ofbusy signals `comprising a series of 3` pulses of a` predetermined`frequency, -usually i about 80 cycles'per minute,"which are impressed luponthe duplex circuit `by operation of the pole changer.

Asis well knownit has hitherto been necessary to establisha fair balancebetween the line cirl pressed on an unbalanced system unbalance currentsarise which may operate `the receiving recuitand the baiancingnetwcfk indunes systems of either type referred to above, in order to prevent thereceiving relay from responding to theoutgoing pulses. `Whensignals:areimlay.` Thus, in the differential duplexcircuit the `currents in the twooperating windings will be unequal orfunbalanced `andthe strongercurrent may operate the relay' In the bridge duplex circuit thepotentials appliedjto the relay winding are unequal and anequalizing orunbalance `the windings and` may current will iiow through operate the irelay.

In accordance witha feature of theinvention,`

the balancing network issimplied and is standmaybe a remote telephonesubscriber's station or a local operators dialing circuit, and to`repeat the pulses over an outgoing line circuit to a r distanttelephone exchange, equipped for automaticswitching in `responseto thedialing pulses for the selectionsof another exchange or another n Therepeating circuit includes a pole changardized to supply a fair balancefor a large variety of line circuits so that it may be manufactured atcomparatively low cost; In accordance with T T the invention the systemis furthermore arranged` sorthat it will be unnecessary to adjust thebalancing networl; to compensate for sporadic vari- 4 ations in the linecircuitsduring ordinary operating conditions including temperature andleakage conditions. This simplification of the balancing network isfurther effective in reducing the largeamount of designing work involvedin the provisionotf'` a large variety of differently ing relayiorapplying twodifferent transmitting 3 x n i i T present day `severedemands for accuracy.

potentials to the line circuitcorrespondirig to the two 'conditions ofthe pulses, namely,` marking and spacing or currentandno current. "Thepulses from the pole `changing relay are pressed upon a duplex circuitincluding the line 1 circuit in one branch and a `balancing circuitinthe other tranen' relayisincluded in the A polar .receivin'gl oduplex'circuit for reception of signals incoming dimensioned balancingnetworksforthe corresponding varieties of -line circuits to satisfytheFor the purposes"just outlined the invention operations, which would`loe due to improper responses bythe receiving' relay during thetranstain average or `predomiriant line conditions among the largevariety of conditions met with in the plant. Such a network may thusprovide an accurate balance for -a large number of lines, but willnecessarily be less accurate in the balancing of line circuits havingdiverging char-, acteristics without, however, establishing a circuitcondition which would result in false operations due to unbalanceconditions caused by line variations or interference.

When the pulse repeating system is idle, the pole changing or sendingrelay will apply an idle condition to thetoll line, which may be assumedto be a spacing or no current condition, the other end of the' linecircuit being assumed to apply a similar condition to the line. Inresponse to the seizure of the repeater station by a calling station oran operator, the po-le changer applies a busy or marking condition tothe toll line. After the transmission of dialing pulses, the distantstation also applies a marking or answering condition to the linecircuit which consequently will operate the polar receiving relay at therepeating station.

After this'condition has been reached, further pulses may be transmittedin either direction over the line circuit. For example, a rering pulsemay be transmitted by the sending station in the form of a pulse whichwill cause the distant exchange to rering the called line; busy flashesmay be transmitted back to the calling line; and switchhook flashes maybe transmitted in either direction.

The polar receiving relay at the repeater station will respond to.incoming pulses fromthe line circuit and will respond to the answering.

condition' imposed upon the line circuit from the distant end byoperating to marking position. Thus, the receiving relay is arranged tocontrol circuit equipment which, in well-known manner, may be arrangedto respond in proper sequence to the traf-c signals, such as fansweringand busy, from the called line. It may furthermore be arranged tofunction in response to dial pulses from the distant station, when thecall is in the opposite direction, for control of the selectingoperation of telephone switches at the exchange with which the repeateris immediately associated.

It will, therefore, be seen that in a sense the repeater operates underfull-duplex conditions, inasmuch as it will operate with either of twopolarities applied to either vor both ends of the line circuit. However,though the repeater is required to operate in both directions, it willoperate only in one direction at a time so that for any particular linecondition the repeater will heroperating on a half-duplex basis.

This particular condition permits the introduction of a feature of theinvention which basically resides in rendering the receiving relayineffective during the transmission of outgoing signals and restoringthe receiving relay circuit to effectiveness upon termination of theretransmission of outgoing signals.

In accordance with amore speciiic feature of the invention, holdingpulses are caused to flow through the receiving relay during thetransmission of outgoing pulses to prevent kick-oifk of the relay, andfor this purpose a holding circuit is connected directly or indiricetlyto one or more windings of the receiving relay only during the sendingconditions. By` this provision any unbalance current from the line andbalancing circuits due to the outgoing pulses will be opposed or itseffect overcome.

In accordance with another specicfeature of the invention, the holdingimpulse circuit includes capacitance means which may be alternatelycharged and discharged for producing the desired holding effect once foreach outgoing transition.

fIn accordance with still another specific feature of the'invention, thedirection of the holding impulses is controlled by the position of thereceiving` relay at any time, as determined by the line potentialapplied at the distant end.

The invention will now be described more in detail as to itsorganization and operation and as applied to specic embodiments. In thedev scription reference will be made to the attached representing aspecic application of the invention and including the features of theinvention; and Y Figs. 5, 6 and 7 are similar circuit diagrams of arepeater circuit representing other specific applications of theinvention and including different modications of the arrangement shownin Fig. 4.

Referring to the drawings, it will be assumed that a subscribers-station is connected to a telephone exchange and desires to make a callto a distant subscribers station at another telephone exchange. The twoexchanges are connected together over toll lines.`

In accordance with established trafic conditions in the telephone plant,the subscriber first removes his receiverl from the hook, therebyestablishing a calling condition. Thereafter the subscriber operates hiscalling dial which transmits the usual groups of dialing pulses. Thedistant exchange then applies an answering condition to the line circuitand rings the` called subscriber, who answers by lifting his receiveroff the hook, thereby establishinga busy condition. If the calledsubscriber should be busy, a continuous series of busy pulses will betransmitted back to the calling station at the rate of pulses perminute. n Other busy conditions, `as for local trunks or distant trunks,are indicated by similar pulses of different frequencies. Upon thedistant subscriber disconnecting prematurely, a rring impulse maybe'transmitted from the calling end of the line circuit. Subscribers`switchhook flashes may be transmitted at any time in either direction.

The diagram in Fig. 1 shows the signaling current in the line circuit atthe time of a call; Thus, when the line circuit is seized, the linecurrent increases from a no current or spacing condition to a steadymarking current condition. Thereafter the marking current is interruptedby the dialing pulses, whereupon the line current remains steady. In thecase of a subsequent rering the line current is momentarily interrupted.Fig. 2 refers to the conditions at the called end 'of the toll line,which normally is applying a Fig. 3 shows conditions at the calledexchange when a busy condition exists in which case the steady markingcondition is interrupted by spacing conditions.

Fig. 4V is a circuit diagram of a repeater circuit n erate shortlyafter. Relay 400 applies battery to the duplex circuit and over the lineto the distant exchange E for operationlof the switch control circuit 49I.

Relay 44u` completes the capacitance circuit through condenser C and acharging'impulse will ow as follows: from plus battery 463 throughrectifier 46| over break contact of relay 460, make contact of relay440, break contact of relay 43|), through the resistance Ra, condenserand inductance, through the lower operatingwinding of relay 45'0 tominusy battery on relay 400. l This current will be in a direction toaid the biasing winding of relay 450 in holding the relay against thespacing contact. Shortlyl thereafter the condenser circuit will beopened by the delayed operation of relay 43B, and condenser C dischargesthrough resistance Rb.`

The subscriber now operates the dial, the contacts of which producespacing impulses, as shown in Fig. l, by short interruptions of theground connection to the line SL. On the arrival of the first impulserelays 400 and 43S release and relay 440, being slow in releasing,remains attracted for a short interval during each short interruption bythe dial. The capacitance circuit is now closed over the make contact ofrelay 440 and the break contact of relay 430, thereby again sending aholding pulse through relay 450; under this condition, however, thecircuit is terminated at ground on relay 400, thereby somewhat reducingthe intensity of the holding impulse which, however, will ber ofrsuicient strength to hold relay 450 in spacing position over anyunbalance` circuit. When relay 440 releases the capacitance circuit isopened and condenser C discharges.

yAt the end of the rst dial pulse relay 400 operates to again applybattery to the duplex circuit; relay 43 remains temporarily retracted;and relay 440 is quickly attracted The impulse circuit through condenserC thus is again completed and a charging impulse applied to relay 450;when relay 430 is attracted, the impulse circuit is again opened andcondenser C discharges through resistance Rb in preparation for thevnext transition. During each pulse series relayfll will repeat eachmarking and spacing transition, and relays 430 and 440 will cooperate tosend ashort holding impulse through relay 450 every time relay 400reaches either one of its contacts; Thus,

with proper delay action of relays 430 and 440, the holding impulsethrough relay 450 may be of suilicient duration to lock relay 45u in itsposition while a pulse transition passes through the windings of relay45E), 'thereby preventing kick-ofi of relay 450 in response tounbalanced currents in the toll lineand the network BN` through theoperating windings of relay 450. Thestrength of theholding impulse may,of course, be deter.- mined` by the battery potentials and by adjustmentof resistance Ra. The shaping of the 'ho-ldving impulse relative to theline transitions may lequipmentY 41) forthe proper receptiongof lthe thebattery connectionto the line.

answering signal. Relay 450 .alsooperatesrelay 460 to reverse thebattery #connections for vthe capacitance circuit. L i The'y desiredconnection may now-be assumed to have been `established land the called`subscriber will be rung by the ringing equipment at the exchange E. Whenthe calledsubscriber answers, the conversation may; be carried` on overa talking circuit, not shown in the drawings,- but which Awould beclosely associated with the toll line TL, as by being included in thesame cable quad or by some composite arrangement. i Y

It will now be assumed that `some special cir,- cumstance arises, as forexample, that'the distant subscriber hangs up prematurely, necessitatingthe sending of further pulses fromthe calling end, for example, a reringpulse, as indicated in Fig. 1. The relay 400 lwould interrupt Relays 430and 440 would again cooperate to senda charging impulse through relay45D. Due to the changed line condition and the .operation o i relay'450'to marking, relay 46|) now'completes the charging circuit from the highnegative battery 464,' rectifier 462, make contact of relay 460', makecontact of relay 440, break contact of relay 430, through the condenserand relay klliill'to ground at relay 400. Thus, the chargingimpulse.will pass through the lower winding of relay450 in a direction to aidthe operating windings and of suiilcient strength to overcome effect ofunbalanced currents, thereby holding relay l45t!` in marking positionduring the` mark-to-space transition. .At the `end of the rering pulserelay 40|] returns to apply battery to the line `circuit; relay 433quickly releases, and relay 440 remains temporarily attracted,thereby'again` completing the holding circuit through relay u -in thesame direction to the lock relay in marking.

Inthe case of a busy lcon-dition existing at the distant end after alldial pulses were transmit-'- ted, a series of pulses, shown in Fig. 3,would be transmitted by the contacts 49|] over the line TL, through thewindings of relay 450 andv network BN to ground, causing relay 450Htooperate in unison with the busy pulses and apply corresponding busypulses to the circuit 410 for:

suitable response. The consequent operation of relay 460 will have no`eiiect upon the condenser circuit.

In the case of a call incoming to repeater station R, relay 450 wouldbeoperated to marking in response to the application of battery at thedistant exchange E to the line.' Subsequent interruptions, as 'by dialpulses, would cause relay 450 to oscillate and. apply correspondingpulses to the Vcircuit 410 for selective operation of switches. Inresponse to this selective operation a switch will ultimatelyconnect'the subscribers Astation S to the repeater station R.` Thisswitch is diagrammatically represented by contacts LF; contacts LF mayalso represent a linei'lnder switch for connecting the subscriberstation to the repeater in response to a call by the subscriber. Withthe subscriber connected in this manner, switchhook flashes ymay bevtransmitted back to the station Ejin the ymanner'already described. A I

In case the subscriber S is busy, the connection at switch LF willremainopen and the circuit 410 may 'be arranged to automatically operatethe key -4Il for application of busy signal from interrupter 4I. RelayV400 will operate in unison with the busy pulses-Wand relays @tand l,`over .contacts l are beyond control.

Vailing` position. f l l Referring now, more particularly to the em- Il.will produce vcorresponding holding impulses for relay 450, as alreadydescribed.

On observing the busy signalpthe distant `call-` ing station at E `willhang up and thus will send a1 disconnect ,signal by applyingsteady-ground 490 through the windings otrelay 4511, thereby Operatingthe relay tospacing.. The` circuit 410 responding to this 'operation`may be arranged to automatically disconnect ,the inter-` rupter 410 bymeanslof contacts 4H., whereupon l wholeV systeinjwill be restored toidle `condi-l` .the

tion.. i e e i The inductance I is .inserted between the vconposeofshapingthe outgoing pulses in any desiredmanner. l l

The purpose ofthe condenser circuit connected .to the local branch ofthefduplex circuit is atv. .tained during thetransrnission .ofoutgoingpulses.` Thus, inV accordance with the invention and as .alreadyexplained above, thekbalancing network the charging impulses through thecondensers Cif is` of l simple` construction and is 4designed so that i`networks of .this kind may be used universally `with toll lines ofdifferent lengths and different l vcharacteristics. It is, ofcourse,within the scope of theinvention that a `few .standardize-d types ofnetwork may be provided, each type to fbef used with lineshavingcharacteristics within comi parativlelywnarrow limits and thedifferenttypes of network supplementing one another to .sat-

.isfy the .requirements of. all types of lines. Thus,

any one network will be connected to `a particular line circuit and may-establish only an approximate balance, and the unbalance may be sopronounced that the .receivingrelayordinarily would l.

`during transmissionofloutgoing pulses. l

It is furthermore well known that long line circuits, as usedin tollservice,` are subject to sporadic variations in their characteristicswhich l Where a` very :close balance is necessary; it has beenthepractice to .continuouslyobserve the line conditions andlcorrespondingly vary the balance by the network. y l

`.By the provision ofrthe holding circuit for. the

receiving relay appreciable. 'leeway is alforded in the. balancing of`this circuit,` thereby permit-ting the use of universal networks `forbalancing over wide rangesane'l` also in special cases obviating theneedyfor continual readjustment of the network. W'Ihus, .during sendingof `pulses the effect ofany unbalanced currents that would flow intransition,`

`5, thecondenser Cl is connected in thecircuit from plus battery 553 atthe relay 560 to ground i l; at relay '.illll.` Condenser `C2 isdischarged through` f `resistance R2. l l. l l. .When relay 5.00olperatesto place battery on theduplex circuit,r`elay 54| will operateto dis- `connect :condenserl and replacefit. by conl denser `C2' so thatalcharging impulse will pass l .through the lower operating Winding of`relay 550 1during .the transition'tirne. `Whenrelay 500 opcrates `backtouspacing, relay l 5,4 ljisreleased, thereby connecting condenser `Clinto the circuit `and causing asimilar charging impulse `torpass throughrelay 55B. e e

.the positions shown.. the hold impulses win` in `both cases be in thedirection .to hold relay 55.0 i

.inspacing` VWith battery supplied to the line circuit at :the .distantend of the line TL, relay 550 will be operatedtomarking and relay 56!)`will .be energized,`` therebyreyersing the direction of l andCZiorholding the relay 550in marking position during the sendingeofcnitgoing` pulses.

. IThe circuit arrangement shown :in` Fig. 6is

imilar .tofthose shown in Eigse and and .is

f particularly ysimilar .to that `in Fig. 5 in having .twolconfdensersCI and C2. includedinthe holdl ing circuit `for relay 650. Thearrangement differs fromthat in Fig. .il mainly in the factjthat .thecapacitance circuit is inductively coupled `to .the local branch oi theduplex circuit.`

Thus, a transformer .T having` tworprimary .l rwindingsconnected inseries with the condensers CI and 02, respectively, has a secondarywindcondenser C2, through one transformer .winding `to intermediatepotential or out of the line circuit or thenetwork due to imbalance.conditions would be overpowered `by the condenser current`and.:tlieyrelay would not beloperated y l l l Byreversing thefbatterypotential for the condenser circuit in yaccordance with the' positionofthe receiving relay it isinsured that the holding impulses will alwayslock the relayin its prebodiment illustrated. in Fig.. 5 ofthe drawings,the` system'is somewhatsimilar to that shown in Fig. 4.and correspondingelements are`corre spondingly numbered in two iigures.` l

In the circuit of Fig. 5 the, capacitance circuit includes twocondensers` `CI andi C2, either of which may. be connected into the`holding cir- `1 cuit. by correspol'idingy operations of relay 51H.`

` 1 Relay `54 I` is included in the dial pulse circuit from thesubscribersstation so. that it willgfollow the operations of .sendingrelay 500 during. dialing as wellas duringthesending of lrering and busysignals.

. Under the. normal conditions `as `shown t at" potentiometer Vcircuit615.

e e .The resulting `charging .current will `produce an .impulse in `thel secondary windingin the transformer which will pass in the pro-perdirection through relay to hold therelay in spacing position. l lDuring" an `outgoing `mark--to-space transition relay '64| will completethe charging circuit through rectier 66|, condenser CI and the otherprimary Winding of. the transformer, which Will )produce aA holdingimpulse through relay B50 in l the same direction as before.`

` `to marking With .battery supplied to the toll .line .TL from thedistant exchange E, relay G50 will operate and relay 66.0`Wi1l beoperated to apply .l negative charging impulses through thetransform'erand, in turn,`reversing` l the` holding :impulse in the secondarywinding of thetransformer and simplification is possible in that. only asingle batteryor other direct current source is necessary for theproduction of lholdingirnpulses unl cipal modiiication Ithat "thereceiving relay der. all conditions. This source may furthermore similarto those described above .withthefprin e 150 is connected through twoseparate windings of the relay..

:In this arrangement the dialing` circuit i SLA .With relays 55D andf560in` e potential `througl'rrectiiier 662 to the two condensers;`alternately, thereby re. l

"versing the direction of the l e through the relay E50'to l holdtherelay in markingposition. l l

It will be noted that with this arrangement a i rbe the common sourcefor. the relayoperations..V

the` holding .circuit for from the subscribers station extends throughrelays 100, 14| and142 which operate in unison in response to diallpulses. By means of the contacts of relays 14| and 142 the condensersCl and C2 are connected in alternation to battery 16| for charging or tovthe holding circuit through the two lower windings of relay 15|! and toground at the contacts of relay 160 for discharging.

With the circuit in the condition shown in the drawings condenser C| isconnected `over the break contact of relay 14 I, through the lowermostholding windingof relay 150 and over the break contact of relay 16D toground; the condenser is originally discharged in this circuit.Condenser C2 is vconnected over the break contact of relay 1412 tobatteryv 16| and is in charged condition.

When the repeater is seized by the subscriber S, relays 18|), 14| and142 'are energized."4 Condenser CLis disconnected from relay 15|] andconnected to battery for charging. Condenser C2 is disconnected frombattery and is connected to relay 150 for discharging through the lowerwinding in a direction to aid the biasing winding in holding the relayto spacing, the discharge impulse coinciding with the charge of the linecircuit TL and the balancing network BN when the armature of relay1|l0`reaches the battery contact.

For the sending of a mark-to-space transition relays 100, 14| and 142release.l Condenser C2 is now connected for charging and condenser C| isconnected for discharging through the lowermcst winding of relay 15|]also in the direction to hold the relay in spacing position.

In answering condition the distant exchange E applies battery to theline circuit, thereby operating relay 150 to marking which, in turn,operates relay 16|). Relay 160 disconnects the lowermost winding ofrelay 150 from the holding circuit and connects the other holdingwinding into the circuit. The connection through this second holdingwinding is such that the discharge im-v pulses from the condensers CIand C2 through the winding `will lock the relay in marking positionduring transmission of both kinds of transitions.

Theproperv relation between the pulse transitions in the du'plex circuitand the holding impulsesfrom the capacitance circuit may be adjusted byadjustment-of the inductances I and L in the two circuits. It is., ofcourse', also possible to slightly adjust the timing of relay 100relatively to relays 14| and 142.

The operation of the type of repeater shown in Fig. 7 has been observedunder various circumstances. For this purpose an oscillograph e' 182 wasconnected into the duplex circuit for observation of the unbalancedcurrents in the duplex circuit. Anotherv oscillograph 183 was connectedinto the capacitance circuit for study of the holding impulses. Atelephone receiver 18| was included in the contact circuit of relay 150for the detection of kick-01T. The balancing network included acapacitance 1 I 5 normally adjusted to 4.5 microfarads for good balance.For the observations the capacitance was adjusted over the range between1.5 and 16.5 microfarads without causing relay 15|) to kick-off. Underthe same line conditions but with the holding circuitfor relay 15|]opened by the switch 1 6, the range of capacity variation withoutcausing kick-01T was only about one-third of that observed between thevalues given above.

It should be understood that the invention may readily be adapted forapplication to a telegraph repeating system with similar advantages,where sending takes place against vtwo different signaling conditionsimposed by the remote station.

What is claimed is:

1. A `two-way signaling system comprising an approximately balanced linecircuit `normally maintained alternately in marking and spacing steadystate conditions, receiving relay means at one end of said line circuithaving contacts `for control of a receiving circuit in response toincoming marking and spacing signal pulses superimposed on said steadystate conditions, auxiliary circuit means including relay `meansconnected to be responsive to outgoing marking and spacing signal pulsesto prevent said control by said contacts in response to unbalancecurrents due to said' outgoing pulses, and switching means connected tobe responsive to incoming -line currentstfor the conditioning of saidauxiliarycircuit means for the proper prevention of said control underboth of said steady state conditions,l said auxiliary circuit meanscomprising an impulse producing circuit `connected to a winding circuitfor said receiving relay means for holding' said receiving relay meansin alternate positions in accordance with said alternate steady stateconditions.

v2. A two-way signaling `system comprisingv an approximately balancedline 4circuit normally maintained alternately in marking and spacingsteady state conditions, receiving relay means at one end of said lin-ecircuit having contacts for control of a receiving circuit in responseto incoming marking and spacing signal pulses superimposed on saidsteady state conditions, auxiliary circuit means including relay meansconnected to be responsive to outgoing marking and spacing signal pulsesto prevent said control by said contacts in response to unbalancecurrents due to said outgoing pulses, and switching means connected tobe responsive to incoming line currents for the conditioning of 'saidauxiliary cir-A cuit means for the proper prevention of vsaid controlunder both of said-steady state conditions, said auxiliary circuit meanscomprising an impulse producing circuit connected to a winding circuitfor said receiving relay meansfor holding said receiving relay means,and said switching means including relay means having contacts connectedfor reversing the holding action by said impulse producing circuit inaci control under both of said steady state condiditions.

cordance with said alternate steady state con- 3; A two-way signalingsystem comprising an approximately balanced line circuit normallymaintained alternately in marking'and spacing steady vstate conditions,receiving relay means having contacts for control of a receiving circuitin response to incoming marking and spacing signal pulses superimposedon said steady state conditions, auxiliary circuit means connected to beresponsive to outgoing marking and spacing signal pulses to prevent saidcontrol by said contacts in response to unbalance currents due to saidoutgoing pulses, and switching means connected to be responsive toincoming line currents for the conditioning of said auxiliary circuitmeans or the proper prevention of said tions, said auxiliary circuitmeans comprising a pulse circuit for producing'oppositely poled impulsesthrough winding means on said receiving relay means for locking saidreceiving vrelay means during the alternating outgoing transitions, andsaid switching means comprising con'- i state conditions.`

`tactl means for" reversing th'e polarityv ofv the locking impulsesthrough said receiving relaymeans in accordance-withsaid alternatesteady state conditions." i Y Q4: A two-way `signaling system comprisingan approximately balanced `linecircuit normally having marking-andspacing steady state conditions alternately appliedtoI theY remote end,receiving relay means at the near endotsaid` line circuit having,contacts for control of a receiving circuit` in `response to incomingmarking andv spacing signal pulses superimposed onsaidl steady stateconditionsyauxiliary circuit means con# nected to be responsivetooutgoing marking and spacing signal pulses tol prevent" said control bysaid' contacts inresponse to unbalance currents due to` said outgoingpulsesyandswitcliing means cuit `connected to a winding 'circuit forsaidre-,-

ceiving relay, means for locking said receiving;

lrelay meansl lnfalternate positions in` accordance withl saidlalternate steady state conditions, said auxiliary`- circuit meansfurther including .quick responsive relaylmeans for closing saidimpulseproducing circuit in4 response to successive trarn` sitions, and`slow-responsive relay means for opening said impulse circuit atianfinstantcbetween successivetransitions; i f

7; Altwo-way signalingsystemcomprisingan approximately balanced linecircuit normally maintainedalternately in marking and spacing steadystate conditions from 1 the remote endl,`

receivingrelay` meanshaving contacts for con-f trol ofl a receivingcircuit in response to incom-` ingmarking and spacing signal pulsessuperimconnected tothe responsiveto said steady state 'conditibns'fcr`conditioning said auxiliary circuit means for the'jprop'er prevention oisaid control underbothof said steady state conditions', said "auxiliarycircuit' meansn comprising Aan impulse f producing circuit connectedlto`a winding onsaid n receiving4 relay means `for` locking said receiving'`relaymeans during outgoing transitions to marking or to spacing, andsaid switching means comprising contact means and polarizing means forreversing the polarity of said impulse producing circuit in accordancewith said alternate steady l5. |A` two-way signaling system comprisingan approximately balanced line circuit normally having markingandspacing steady stateconditions alternately applied to the remote end,receiving relay means at the near end of` said line y circuit havingcontacts for controlof a receiving winding onvsaid receiving relay meansfor locking said receiving relay means, and including ca- `pacitancemeans for producing unidirectional impulses for said locking during eachoutgoing transition, and said auxiliary circuit means further comprisingcontact means for completingL said impulse producing circuit once foreach out-` going transition. i

n 6. A two-way signaling system comprising an approximately balancedline circuit normally maintained alternately in marking andspacingsteady state conditions from the remote end,`

receiving relay means having contacts for `control of a receivingcircuit in response to incoming 4marking and spacing signal pulsessuperimposed on said steady state conditions, auxiliary circuit meansconnect-ed to be responsive to outgoing marking and spacing signalpulses to prevent said control by said contacts in response n tounbalance currentsdue to said outgoing pulses, and switching means`connected to l to said steady state conditions for the condii tioningof said auxiliary circuit means for the i proper prevention of saidcontrol" under both of `said steady state conditions, said auxiliarycirfcuit means comprising an impulsevproducing cirbe responsive i posed onsaid! steady state conditions," auxiliary circuit means connected tobeiresponsive to outgoing marking and` spacing signal pulses topreventsaid` control by said contacts in `response tounbalance``currents due to said `outgoing pulses, and switching meansconnected.`to berrespcnsive to saidfsteady stateconditions for conditioningf `saidauxiliary circuit lmeans for `the proper 'preventionofsaid control underboth of said steady state conditions, saidauxiliary circuit meansLcomprising an `impulse circuit con- .nectedto a, Winding circuit forsaid receiving re-` lay means for locking said receiving relay means inalternatepositions in accordancewith said al` ternate steadystateconditions, said impulse circuit includingtwo self-dischargingcapacitance circuits for producing unidirectional impulses for saidlocking, and said auxiliary circuit means further including relay meansfor `completing said impulse circuit alternately through said two ca-ipacitance circuits during alternate outgoing trani sitions. n i n n 8. Atwo-way signaling system comprising an approximately balanced linecircuit normally` vmaintained alternately in marking and spacing steadystate conditions from the remote end, receiving relay means havingcontacts for con-` trol of a receiving `circuit in response to incomingmarking andspacing signal pulses superimposed on said steady stateconditions, auxiliary circuit meansconnected `to be responsive to out` igoing marking and spacing signal pulses to prevent said control by saidrelay means contacts in response to unbalance currents due to saidoutgoing pulses, and switching means connected to be responsive to saidsteady state conditions for conditioning said auxiliary circuit meanstor the proper prevention of said control under both of said steadystate conditions, said auxiliary cir-` cuit means comprising an impulsecircuit con-V nected to a windingcircuitfor-said receiving relay meansfor locking said receiving relay means inalternate positions in`accordance with said al-` ternate steady state conditions, said impulsecirwcuit including inductance means for producing y unidirectionalimpulsesfor said locking, and said auxiliary circuit means furtherincluding `contact means for closing said impulse circuit once n `foreach outgoing transition.

`9. A two-way signaling system comprising an approximately `balancedline circuit,` normally` maintained alternately in marking and spacingsteady stateconditions from the remote end, re-

i ceiving relay means having contacts forcontrol of a receiving circuitin response tol incoming marking` and spacing signal pulses superimposed`on said steady state conditions, auxiliary cir cuit means connected `tobe responsive to outgc vention of said control under both of said steadystate conditions, said auxiliaryl circuit means comprising an impulsecircuit connected to a winding circuit for said receiving relay meansfor locking said receiving relay means in alternate positions inaccordance with said alternate steady state conditions, said impulsecircuit including two capacitance circuits and a charging sourcetherefor for producing impulses for said locking, and said auxiliarycircuit means further includingl relay means for alternately chargingsaid condensers and discharging them in said irnpulse circuit for saidlocking during each outgoing transition to marking and spacing.

10. A two-Way signaling system comprising an approximately balanced linecircuit normally maintained alternately in marking and spacing steadystate conditions -from the remote'end, receiving relay means havingcontacts for control of a receiving circuit in response to incomingmarking and spacing signal pulses superimposed on said steady stateconditions, auxilitry circuit means connected to be responsive tooutgoing marking and spacing signal pulses to prevent said control bysaid relay means contacts in response to unbalance currents due to saidoutgoing pulses, and switching means connected to be responsive to saidsteady state conditions for conditioning said auxiliary circuit meansfor the proper prevention of said control under both of said steadystate conditions, said auxiliary circuii-l means comprising an impulsecircuit connected to a winding circuit for said receiving relay meansfor locking said receiving relay means in alternate positions inaccordance with said alternate steady state conditions, said impulsecir-4-` cuit including two inductance circuits for prof ducing similarlydirected impulses for said locking during each outgoing transition tomarking and spacing, and said switching means includin'g relay meansconnected for reversing said impulses for said locking corresponding tosaid steady state conditions. o

ROY B. SHANCK.

